1. Field of the Invention
The present invention relates to a black matrix, and more particularly, to a method for forming a black matrix for a cathode ray tube (CRT) having excellent landing margin and blackness by a non-etching method.
2. Description of the Related Art
Generally, green, red, and blue phosphors are regularly arranged in a dotted or striped pattern in the inner surface of a color CRT, and electron beams irradiate onto a target dot or stripe to make the corresponding phosphor luminesce.
However, the electron beams do not irradiate onto a target dot or stripe exactly but an adjacent phosphor dot or stripe of another color may also luminesce, which lowers color purity. Also, a fluorescent layer may luminesce due to electrons scattering at the inner wall of a panel or around shadow mask apertures, which causes lowering of contrast.
To avoid such lowering of color purity and contrast, generally a non-luminescent absorbent such as graphite is filled in a space between the respective phosphor dots or stripes to form a black matrix.
A black matrix is largely classified into a negative black matrix and a positive black matrix according to the size of a phosphor dot or stripe and the size of an electron beam irradiating onto a dot or stripe.
According to the negative black matrix, the irradiated beam is made larger than the phosphor dot or stripe, a landing margin is excellent, and contrast and luminance can be improved. However, if the black matrix size between the red, green, and blue phosphors cannot be adjusted uniformly, a poor quality screen, e.g. a color blot, is liable to be generated.
The negative black matrix is generally fabricated in the following manner.
First, a negative photoresist forming composition comprising a base resin, a binder, a dispersant, and a hardening agent are applied to the inner surface of a panel of a CRT and dried to form a photoresist layer. Then, the photoresist layer is exposed to light and developed so that an exposed portion where phosphor patterns are to be formed is hardened by a photo-reaction, to thereby form a photoresist pattern having a strong adherence to an underlying layer (here, the inner surface of the CRT panel) and being not developed by water.
Subsequently, graphite is applied to the photoresist pattern to form a black matrix layer. Then, etching and developing processes are sequentially performed to remove the exposed portion of the photoresist layer and the black matrix material layer on the exposed layer, thereby completing a black matrix pattern.
As described above, the negative black matrix is, however, formed through a long and complicated process line, and requires an etching step in which materials detrimental to the environment are used.
Also, manufacturing cost is too high to use Ti-containing black pigment composition which can form a black matrix having excellent blackness.
On the contrary, according to a positive black matrix, the irradiated beam is made smaller than the phosphor dot or stripe. Although an excellent landing margin is not easily obtained, the positive black matrix is advantageous in being easily fabricated without an etching step. However, since a photoresist forming material suitable for this method is not in practical use, the positive black matrix is not widely used.